Slab Foundation Repair in Cary

Some Cary homes, garages and additions sit on slabs. Clay movement can settle slabs or crack them.

This guide covers repair options.

Signs

Cracks in the slab or brick, gaps at doors and windows, and uneven floors.

Options

Mudjacking lifts sunken non-structural slabs ($500–$2,000 published). Underpinning with piers supports foundations ($3,000–$15,000 published).

Clay soil

Moisture changes in clay drive settlement; drainage and gutters reduce movement.

Keep soil around the slab edge at a steady moisture level where practical: extend downspouts, slope soil away from the house, avoid overwatering beds right against the foundation, and keep large trees' roots in mind, since they draw moisture from clay during droughts. Garages and additions built on separate slabs can move differently from the main house, so cracks often appear where they meet.

Engineering

Structural repairs need a PE per NC BELS.

Permits

Foundation repairs need a permit in Cary; new foundations may need as-built surveys under the LDO.

Choosing a repair

Mudjacking and foam lifting are typically for driveways, patios, walks and garage floors; foundation footings that carry the house usually need piers designed by an engineer. Ask each contractor what their method is designed to support and what happens if movement continues.

Diagnosing slab problems

Not every crack means settlement. Concrete shrinks as it cures, so thin hairline cracks are common and often cosmetic. Cracks that widen, offset vertically or let water in, and floors that slope, deserve evaluation. Doors that stick, gaps between walls and ceilings, and stair-step cracks in brick veneer can point to foundation movement. An engineer can measure elevations and determine whether a slab is settling, heaving or simply cracked. Plumbing leaks under a slab can also soften soil, so a plumber's pressure test may be part of the investigation.

Warning signs worth a professional look

Some changes in a Cary home are routine seasonal movement; others point to a problem that grows if ignored. Have a professional look when you notice cracks wider than a credit card or cracks that grow over months, stair-step cracks in brick or block, doors and windows that suddenly stick or will not latch, floors that slope or feel soft, gaps between baseboards and floors, standing water or a musty smell under the house, sagging or wet insulation, condensation on ducts or pipes, or wood that feels soft when probed. Take dated photos with a ruler or coin for scale so you can show changes over time. Note whether symptoms change after heavy rain or long dry spells, since that pattern helps separate drainage and moisture problems from structural settlement.

Slab-on-grade in Cary

Most Cary homes sit on crawl spaces, but garages, additions, sunrooms and some newer homes are slab-on-grade. Slabs on Piedmont clay can heave when soil swells and settle when it shrinks or when soil softens around a plumbing leak. Angi's crawl space repair guide lists mudjacking at $500–$2,000 and underpinning at $3,000–$15,000, with piers at $1,000–$3,000 each.

Plumbing leaks under slabs

A leaking supply or drain line under a slab can wash out or soften soil and cause localized settlement. Signs include unexplained water bills, warm spots in the floor, damp flooring and the sound of running water. A plumber's leak detection test is often worth doing before structural repairs.

As-built surveys for new work

If repair work extends to new foundations, such as replacing a slab addition, the Town of Cary's Land Development Ordinance may require a sealed as-built foundation survey for residential structures near setback lines, buffers or easements. Ask the Town early.

Choosing the repair

Repair choice depends on the cause. Slabs that settled because soil was washed out by a leak or poor drainage may be lifted and stabilized after the leak is fixed; slabs that keep settling on weak soil may need piers. Polyurethane foam injection is another lifting method contractors offer for slabs. Ask the engineer which approach fits and why, and how long the repair is expected to last.

Interior cracks in tile and gaps at baseboards are common symptoms, but they do not always mean structural failure. A structural engineer's evaluation, which Angi prices at about $350–$800, separates cosmetic cracking from structural movement before you spend on repairs.

Garages and additions

Garage slabs and add-on rooms often move separately from the main house because they sit on different footings or fill. A crack at the joint between an addition and the original house may reflect that difference rather than failure of either foundation.

Keeping records

Keep the engineer's report, leak test results, permit records and warranty together; future buyers and inspectors will ask. If flooring must be removed to repair a slab, ask whether the flooring work is included or will be a separate cost, and who handles replacement. Clarify cleanup and debris removal in the contract as well.

Before agreeing to lift a slab, ask whether lifting could reopen cracks in tile or drywall and whether the contractor will survey floor levels before and after, so you can see how much correction was actually achieved.

Published crawl space and foundation cost estimates

Sources: Angi: Crawl space repair cost (2026); Angi: Crawl space dehumidifier cost (2026); Angi: French drain cost (2026); Angi: Structural engineer cost (2026). Figures are published national or regional estimates compiled by those sites, labeled as estimates; they are not quotes and not prices from any provider on this site. National published estimates; Cary crawl spaces with low clearance, standing water or extensive wood damage price toward the upper end. Engineering and permits are often separate.

Local rules and code references

• Town of Cary Residential Permits & Inspections FAQ: lists foundation repairs, and closing or sealing a crawl space, among residential projects that require a building permit, quoting the NC State Building Code requirement to obtain a permit before altering or repairing a structure.
• NC Board of Examiners for Engineers and Surveyors, Foundation Repair Guidelines (rev. 10/22/2024): state board guidance: a PE must be in responsible charge of foundation evaluation, pier count and location, repair design and completion certification.
• Town of Cary Land Development Ordinance §3.14.2(D), as-built foundation surveys: sealed as-built foundation survey by an NC-registered land surveyor for residential structures, with exceptions such as buildings five feet or more from any setback line, buffer or easement.

Code text and department procedures change; confirm current requirements with the jurisdiction before work starts.